1. Field of the Invention
The present invention relates to a wiring board including an inductor, a method of manufacturing the same, a tuner module, and an electronic device.
2. Description of the Related Art
Silicon tuners achieving a function of receiving television broadcasts with an analog high-frequency circuit integrated in a semiconductor such as Si (silicon), SiGe (silicon germanium) or the like have recently been actively developed. Silicon tuners have a feature of a greatly reduced volume as compared with box-type modules of “CAN tuners” in the past. CAN tuners have a large volume because not only an IC (Integrated Circuit) of a mixer, a PLL (Phase Locked Loop) circuit and the like but also a large number of analog parts including an air-core coil having a diameter of a few mm which air-core coil forms an analog section such as a filter or the like and a varactor diode are mounted within a metal for shielding.
Silicon tuners realize miniaturization by integrating these analog parts into an IC. However, when a filter function is integrated into an IC, it is difficult to enhance the performance of a filter as compared with CAN tuners because a coil that can be integrated into an IC has a small diameter of a few μm. Thus, in employing a silicon tuner, it is difficult to enhance receiving sensitivity because of a difficulty in sufficiently removing an undesired signal by a filter.
Accordingly, a method is known which enhances receiving sensitivity by mounting a winding inductor as an external part on a board separately from a silicon tuner (IC). However, when the external part is mounted on a printed wiring board or an interposer board, a wire bond and board wiring have to be routed from the silicon tuner and connected for electric connection between the silicon tuner and the external part. Thus, inductor characteristics are degraded due to effects of parasitic resistance, parasitic capacitance, and parasitic inductance of the wiring and the like. In addition, costs such as the parts cost of the external part, a mounting cost and the like are added to the cost of the tuner.
As one of techniques for solving such problems, a technique is known which forms the coil of an inductor by wiring of a printed wiring board or an interposer board. This technique can substantially shorten a distance of routing of wiring, and suppress degradation in inductor characteristic due to parasitic resistance and parasitic inductance. However, this technique has problems of increasing parasitic capacitance between the wiring and other wiring in the board and decreasing the self resonance frequency of the inductor.
Accordingly, for example Japanese Patent No. 2898814 (referred to as Patent Document 1 hereinafter) describes a constitution as a constitution of a “multilayer wiring board with a printed inductor” in which a part or all of a ground layer, a wiring layer, or a power supply layer situated directly below or directly above a printed inductor included in the multilayer wiring board is cut away. This constitution equivalently increases a distance between the ground layer, the wiring layer, or the power supply layer and the printed inductor by the presence of the cutaway part. Thereby, the parasitic capacitance of the inductor is reduced, and a decrease in the self resonance frequency of the inductor is prevented.